At present, standard methods for monitoring airborne asbestos fibers are based on filter sampling techniques. In such methods, asbestos fibers are collected on filter and are subsequently analyzed by optical or electron microscopy or chemical methods in order to determine asbestos concentration. These general methods suffer from several drawbacks, such as delayed availability of information, tediousness, inconvenience, high cost per sample, lack of precision, etc.
Although it is recognized that filter sample/microscopy techniques will most likely continue to be regarded as reference tools, there is a clearly established need for a real time asbestos monitor. This need is clearly demonstrated by the common practice of using the Fibrous Aerosol Monitor ("FAM-1") available from Monitoring Instruments for the Environment ("MIE"), Bedford, Massachusetts, for routine auxillary monitoring during and after asbestos removal and/or containment operations. The FAM-1 is a rugged and reliable field-worthy monitor capable of withstanding the rigors of asbestos removal operations. The FAM-1 samples the environment and simultaneously subjects the aerosol sample to constant and time-varying electric fields to align and oscillate the fibers while illuminating the fibers perpendicularly to their axes with polarized light. The pattern of light perpendicularly scattered by the aligned and oscillated fibers makes it possible for the FAM-1 to identify and count the number of fibers in the sample on a real time basis. The principles of operation of the FAM-1 to obtain fiber alignment and periodic oscillation are described in "Rotational Electrodynamics of Airborne Fibers", Lilienfeld, J. Aerosol Sci., Vol. 16, No. 4, pp. 315-322 (1985). The principles of operation of the FAM-1 optical system are illustrated and described in "Light Scattering From Oscillating Fibers At Normal Incidence", Lilienfeld, J. Aerosol Sci., Vol. 18, No. 4, pp. 389-400 (1987).
The FAM-1, however, is incapable of distinguishing asbestos fibers from other types of fibers, e.g. glass, polymer, cellulose, textile, etc. In addition, the FAM-1 is only capable of detecting fibers longer than 2 micrometers with diameters as small as 0.1 micrometers, whereas current Environmental Protection Agency ("EPA") requirements call for detection of fibers as short as 0.5 micrometers with diameters less than 0.1 micrometers. To date, however, the FAM-1 provides the only practical real time aerosol monitor for auxillary asbestos fiber monitoring.
Therefore, it is one object of the present invention to provide a real time asbestos monitor.
Another object of the invention is to provide a real time asbestos aerosol monitor capable of identifying asbestos fibers and distinguishing such asbestos fibers from other types of fibers.
Yet another object of the present invention is to provide a real time asbestos monitor capable of identifying and counting asbestos fibers as short as 0.5 micrometers with diameters less than 0.1 micrometers.
These and other highly desirable and unusual results are accomplished by the present invention in a compact, portable real time asbestos aerosol monitor capable of identifying asbestos fibers and distinguishing asbestos fibers from other types of fibers for counting.
Objects and advantages of the invention are set forth in part herein and in part will be obvious herefrom, or may be learned by practice with the invention, the same being realized and attained by means of the instrumentalities and combinations pointed out in the appended claims.
The invention consists of the novel parts, constructions, arrangements combinations, steps and improvements herein shown and described.